Rocker Arm Questions

kenewagner

Registered User
Just for my own information and what I know. The 1.6 is the stock rocker arm ratio for our beloved 3.8, correct? I know some are running 1.73 ratio which gives more lift to the cam, correct. Does the 1.73 ratio mess up to any extent the geometry of the vave train? Does it put more strain on valve train parts as it seems it that it would have less mechanical advantage than a 1.6. I figure that a lot of people move to the 1.73 rocker to gain more valve lift without changing the cam. Would not a 1.6 rocker be a better choice, if installing a new cam and than installing a cam with more lift to meet your expectation of a final lift number. I am just looking for good information and schooling at this point;)

Ken
 
If it is the engine I am thinking of maybe it has to to w/ the type of cam it has. But that is a complete and total guess! Sometimes I just like to post and say Hi!:D

Stephen
 
The actual rocker ratio is not really the important factor. Chevy's use 1.5 for their small block V8 and have done so since 1955 or so. As long as the cam is ground with the right rocker ratio in mind, things will work themselves out. The important thing is how consistent the ratio is and the alignment of all related parts.

Since a valve moves in a linear motion whereas the rocker arm moves in a circular motion, a certain amount of lift is always going to be lost due to the horizontal travel of the roller tip. Minimizing this movement helps maximize the actual valve lift compared to theoretic lift due to the cam lobe. It is ideal to have the rocker sweep a .060" path on the tip of the valve, starting to the inside of center, sweeping out, and then coming back in at max lift. The only way to verify proper fitment/application is to actually observe this movement on your valve tips. You can't rely on anyone else's statements or advertising claims.

Another and more important aspect of tip alignment is that if the rocker arm is traveling across the tip of the valve more than it needs to, it is also "pushing" against the valve which wears out valve guides, particularly if the pushing motion occurs when the valve is at maximum lift where the point of rocker arm contact is under the most pressure.

There is a whole science to valve train and rocker arm geometry. Take a look at this site www.mid-lift.com for a more in depth explanation of what I'm referring to.

The SC engine does use a 1.73 (approximately) ratio as did Ford on the 351C and 460 family motors. The SC pedestal mount system is designed for the stock .450" lift and when higher lifts are prescribed, the geometry that Ford worked out starts to go out the window. Watching and understanding how this goes is important in deciding the right components to use for a custom rocker arm system. The 351C/460 rocker arm is not a perfect match for the SC but it's close. Close enough that people have been using these rockers for nearly all 3.8L applications and in fact the rocker arms that are sold by some vendors as being "3.8L applications" are really nothing other than 460 rockers with metric bolts supplied. Seriously. No one makes a rocker arm specifically for the 3.8L engine.

Some people have used 302 Ford rocker arms because the 5.0 also employed a pedestal system. These rockers are typically 1.6 but can also be found as 1.7 and 1.72 ratio. These rockers will bolt on but they are typically not the correct reach and geometry for our motors. That doesn't mean they can't be used because like I said, valve tip height, pushrod length, and other factors could make them a viable application if everything is set up right. I've never tried to use them because I prefer not to make things more complicated than they already are, so I stick to the 460 style rocker arms.

In a most basic sense, when selecting rocker arms and pushrods, most people just look for something to take up the proper clearance and call it good. For many people that is a big enough job in itself. But if you really want to get the most out of your system then you need to look at tip alignment and travel. You may find that you need to run a quite different set of parts than you originally thought to get things to work out correctly.

In many cases it is not even possible to set up geometry for ideal contact, but, for example, with David's setup we had all the right components to be able to end up very close to ideal which should maximize cam performance as well as valve guide life. Adjustable stud mounted rocker arms can actually be some of the most difficult to set up and get right. Much as many people curse the shims necessary to set up a pedestal system, the pedestal system is actually better than a stud mount system and is much easier to set geometry on if you know what you are looking for.
 
When looking at my heads would you need all the rockers left in place to observe each indiviual piece or just one to check its geometry.

Ken
 
Dave when everyone was getting into group buys for 1.73 rockers the vendors advertised it gave slightly more lift then stock. What is the exact ratio of a stocker. Was this false advertisement?
 
.....Another and more important aspect of tip alignment is that if the rocker arm is traveling across the tip of the valve more than it needs to, it is also "pushing" against the valve which wears out valve guides, particularly if the pushing motion occurs when the valve is at maximum lift where the point of rocker arm contact is under the most pressure....

I have no idea what these guys are talking about, It all sounds a little naughty to me... Try substituting 'rocker arm' for penis, and 'valve' for vagina in the above post... :D

See what I mean?

Sorry Ken, Sorry Dave...spring is in the air!
 
Dave when everyone was getting into group buys for 1.73 rockers the vendors advertised it gave slightly more lift then stock. What is the exact ratio of a stocker. Was this false advertisement?



This is a great question. So if the stock ratio is 1.73 why would anyone buy the scorpion rocker arms? I feel like this might be a crazy question. Am I missing something?:confused:

edit: I dug around, I see they are good for about 0 HP but if running a more aggressive cam they would be a great upgrade for durability. Pointless for a stock rebuild
 
Last edited:
This is a great question. So if the stock ratio is 1.73 why would anyone buy the scorpion rocker arms? I feel like this might be a crazy question. Am I missing something?:confused:

edit: I dug around, I see they are good for about 0 HP but if running a more aggressive cam they would be a great upgrade for durability. Pointless for a stock rebuild

Because they use rollers and bearings to reduce friction, and the stock rocker arm doesn't.

David
 
Because they use rollers and bearings to reduce friction, and the stock rocker arm doesn't.

David

Right but it's my understanding that they use needle bearings and those can crap out leaving us with another point of failure. Pros and Cons to consider
 
Right but it's my understanding that they use needle bearings and those can crap out leaving us with another point of failure. Pros and Cons to consider

I don't think they are worth using on a stock motor, but when using a more agressive cam profile, higher sprinf loads and increased rpms they are a worthwile investment. Anything can break, and I would trust a set of Scorpion roller rockers to hold up a lot better than the stocked stamped steel rockers.

David
 
Back
Top